Airbag Warning Light On: Causes and Diagnostics

If the Airbag light has come on, it indicates that the airbags are currently disabled and will not deploy in an accident. The icon may stay on continuously or flash, indicating an active error code in the SRS control unit.

The Supplementary Restraint System (SRS) includes not only the airbags themselves but also:

• seat belts with pretensioners;
• pyrotechnic charges;
• impact sensors;
• the control unit (ECU).

If the indicator (a figure with an airbag or the letters SRS) lights up on the dashboard, the system has detected a fault in one of these components or a communication failure between them.

Why does the Airbag indicator light up?

When the ignition is switched on, the control unit performs a self-diagnostic: the light comes on for a few seconds to check circuit integrity. If the system is working correctly, the indicator goes out. If the light remains on or starts flashing, a fault code is stored in memory.

Sometimes the error is intermittent. In this case, the light may go out after restarting the engine, but the error code will remain in the control unit's history. If the fault is critical and permanent, the indicator will stay on until the fault is rectified and the error is cleared with a scanner.

Possible Faults

Modern safety systems are reliable, so electronic 'glitches' are rare. If the SRS light is on, the problem is most likely physical.

Locations where Airbag safety system faults occur

Main causes for the indicator lighting up:

1. oxidised contacts in connectors (the most common cause);
2. problems with connectors under the front seats (often disturbed when cleaning the interior or adjusting the seats);
3. damage to the spiral cable (clock spring/rotary coupler);
4. impact sensor failure (often due to corrosion after washing or dampness);
5. broken wiring between the unit and the airbag;
6. SRS fuse failure;
7. control unit malfunction (e.g. due to voltage drop);
8. errors when installing an alarm or stereo system (damaged wires);
9. previous system deployment (requires airbag replacement and unit reprogramming/replacement);
10. low onboard network voltage (old battery);
11. expiry of pyrotechnic charges (usually over 10-15 years).

Diagnosing the Spiral Cable (Clock Spring)

A frequent cause of the driver's Airbag error is a broken spiral cable (clock spring). The cable constantly winds and unwinds as the steering wheel turns and eventually breaks or wears out.

Indirect signs of a faulty clock spring:

• steering wheel buttons stopped working simultaneously with the SRS error;
• the horn has stopped working;
• a crunching or rustling sound is heard when turning the steering wheel.

Procedure and Rectification

It is difficult to repair the system yourself, as working with SRS requires a scanner capable of reading this unit (standard cheap ELM327 devices often do not see airbag errors).

What you can do yourself:

1. Check battery charge. Low voltage can cause false errors.
2. Inspect connectors under the front seats. Often just adjusting the plugs (with the ignition off!) is enough to restore contact.
3. Check the fuses responsible for the Airbag.

Professional diagnostics:

1. Connecting a scanner, reading the error code (e.g. 'Driver pretensioner circuit open').
2. Localising the problem according to the code.
3. Wiring repair, replacement of the spiral cable or sensor.
4. Software error reset.